Chapter05 Immunoglobulin

Chapter5Immunoglobulin Contents IntroductionSection MolecularStructureofIgSection CharacteristicsandFunctionsofthe5ClassesofIgSection FcReceptorsforAbMoleculesSection BiologicalActivityofAbSection ImmunogenicityofIgSection ArtificialAb Concepts Antibody Ab GlycoproteinmoleculesthatareproducedbyplasmacellsandcancombinewiththecorrespondingAgspecificallyarecalledAb AbisproducedbyBcellsintheresponsetoastimulationofAg Abpossessesahighdegreeofspecificityandaffinity Immunoglobulin Ig ItreferstoallglobulinsthatpossesstheactivityofAborshowasimilarstructuretoAbTherefore AllAbsareIgs butnotallIgspossessthefunctionsofAbs OtherConcepts GlobulinAntiserumHumoralImmunitysIgandmIg BCR Section MolecularStructureofIg Basicstructure IgiscomposedoffourpolypeptidechainsjoinedbyS Sbonds inter chaindisulfidebonds S S intra chaindisulfidebonds S S Itshows T or Y shape fourpolypeptidechains 1 HandLchain Heavychains H 450 550aa 50 75KD Lightchains L 214aa 25KD Twoterminalendsforeachpeptidechain N terminalend C terminalendLchainsattachtoHchainsfrom N end N C 2 classesandtypesofIg 1 AccordingtothedifferencesofHchains aminoacidcomposition sequence Igscanbedividedinto5classesFiveclassesofHChain FiveclassesofIgs IgGIgAIgMIgDIgE subclasses IgG1 IgG4 IgA1 IgA2 2 AccordingtothedifferencesofLchainsTwotypesofLchain 20 1 inmice 2 1 inhuman subtypes 1 4 3 Tworegionsofeachpeptidechain 1 Constantregion C 3 Hingeregion 2 Variableregion V 1 Constantregion C CH 3 4or4 5 ofHchainfromthecendCL 1 2ofLchainfromthecend 2 Variableregion V CH 1 4or1 5 ofHchainfromtheNendCL 1 2ofLchainfromtheNend 3 Tworegionsofeachpeptidechain 2 Variableregion V Hypervariableregion HVR TherearethreehighlydiversitystretcheswithintheVegion theyarecalledHVR Frameworkregion FR FR1 FR4 Ag bindingsites Complementaritydeterminingregions CDR 2 Variableregion V Complementaritydeterminingregions CDR L CDR1 CDR2 CDR3H CDR1 CDR2 CDR3 IdiotypeofIg IgsproducedbydifferentBcellspossessuniquestructurerespectivelyinhypervariableregion HVR theuniquestructureofIgiscalledidiotypeoridiotypicdeterminant Infact HVRCDRIdiotypeareinthesamesitesofIg 3 Hingeregion FlexibleandsuitableforCDRofIgbindingtoantigenicdeterminants SensitivetoproteolyticenzymeIgM IgE OtherstructuresofIg Joiningchain J Secretorypiece SP Joiningchain J ProducedbyplasmacellsFunctions linker tocomposedimer pentamerorpolymer IgA IgM Secretorypiece SP Producedbymucosaepithelialcells SecretoryIgA sIgA Functions protectsIgA resistproteolysisinextrasecretoryliquid IgA DomainsofIg 1 Domain PolypeptidechainsofIgarefoldedintoaglobularstructurebyintrachains sbondwithineach110aaregionwhichiscalledadomain 2 DomainsofIg Lchain 2 VL CLHchain 4 5 VH CH1 CH2 CH3CH4 inIgM IgE hingeregion 3 Functionofeachdomain VH VL antigen bindingsiteCH1 CL allogeneicmarkerCH2 CH3 complement fixingsite permeateplacenta IgG CH3 CH4 cell bindingsiteHingeregion flexibleandsuitableforCDRofIgbindingtoantigenicdeterminants HydrolyticfragmentsofIg IgcanbedigestedbypapainandpepsinPositionFragmentsFunction 1 Digestedbypapain Position neartheS SbondsofHinter chainsfromtheNendFragments 2Fab fragmentantigen bindingFc fragmentcrystallizableFunction Fab recognizeandbindAgFc 1 fixcomplement 2 crossingtheplacenta 3 bindtoFcRindifferentcells Ag Abratio 2 DigestedbypepsinPosition neartheS SbondofHinter chainsfromtheCendFragmentsandfunction F ab 2 bindantigen 2valence pFc nofunction Significance ElucidatingtherelationshipsbetweenthestructureandfunctionofIgsDecreasetheimmunogenicityofIgforclinicaltreatment Section CharacteristicsandFunctionsofthe5ClassesofIgs IgG 1 Highestconcentrationinserum 75 oftotalIg 2 Foursubclasses IgG1 IgG2 IgG3 IgG4 3 UniqueIgthatcanpassthroughplacenta4 Half lifeislonger 16 24days 5 Startstobeproducedat2 3monthafterbirthandreachthelevelofadultat5yearsold 6 FunctionsofIgG Againstbacteriaandvirus neutralizetoxinCombinewiththeFcreceptor Fc R ActivatecomplementCombinewithSPASomebelongtotheauto antibodiesTakepartintype and hypersensitivity IgM 1 HighestMW pentamer 90KD 10valences 2 Half lifeisshorter 4 5days 3 ThefirstIgtobesynthesizedAppearintheearlystageafterinfectionBeproducedduringfetusThefirstmIgoftheBcells actastheantigenreceptors BCR 4 Functions IgMismoreeffectiveinbindingAgandactivatingC andplayanimportantroleinanti infectionNaturalAbforblood typeantigenAuto antibody rheumatoidfactor RF Takepartintype and hypersensitivity IgA1 TwotypesSerumtype monomerSecretarytype sIgA dimer trimerorpolymer2 Twosubclasses IgA1 IgA2 3 Tobeproducedat4monthsafterbirth4 Existinalmostallbodyfluid 6 Localmucosalimmunity ImmunebarrierNeutralizevirus toxinRichincolostrumActivateCbyalternativepathwayTakepartintype hypersensitivity IgD 1 Theconcentrationinserumislowandsensitivetoproteinase2 ActastheantigenreceptoronBcells mIgD RegulatethedifferentiationofBcells IgE 1 ConcerntrationofIgEinserumisthelowestinnormalindividual butisveryhighinsomepatients 2 Relatedtotype persensitivityFc R mastcell basophil Section FcReceptorsforAbMolecules IgG Fc R Fc R CD64 phagocyteFc R CD32 immunecomplexFc R CD16 NK macrophage TcellIgE Fc R Fc R mastcell basophilFc R macrophage BcellIgA Fc R CD89 phagocyte neutrophil Section BiologicalActivityofAb 1 Recognizeandbindtoantigenspecifically2 Fixcomplement3 BindtoFcreceptoronsomecells4 Transferselectively Plancetatransfer IgG Mucosatransfer sIgA AffinityandAvidity Neutralization IgM IgG1 3 classicalpathwayIgA IgG4 IgE alternativepathway MAC 1 Opsonization IgG IgM EnhancethephagocytosisofM 2 ADCC antibodydependentcellmediatedcytotoxicity 3 Hypersensitivitytype mastcell basophil Fc R Section ImmunogenicityofIg Isotype CH CL Allotype CH CL Idiotype VH VLAnti idiotypeantibody Section ArtificialAb PolyclonalAbMonoclonalAbGeneengineeringAb 1 PolyclonalAb AmixtureAbwithdifferentspecificitiesandaffinitiesGenerateinanaturalresponseorartificialimmunizationCrossreaction Cross reactivity iftwoantigensshareanepitopeanantibodyrecognizesanunrelated butchemicallysimilar epitope 2 MonoclonalAb mAb Abproducedbysingleclone oronehybridomasclone andhavingasinglespecificity mAb McAb Preparedbyhybridomastechnique Immunizedspleencells B hybridewithmyelomacells hybridomas Artificialantibodies DerivedfromdifferentBLymphocytescelllines POLYCLONAL MONOCLONAL DerivedfromasingleBcellclone BatchtoBatchvariationaffectingAbreactivity titre mAbofferReproducible Predictable PotentiallyinexhaustiblesupplyofAbwithexquisitespecificity Enablethedevelopmentofsecureimmunoassaysystems NOTPowerfultoolsforclinicaldiagnostictests Cellfusiontechnique Hybridomacell NoAbLonglife SecreteAbShortlife SecreteAbLonglife K hlerandMilstein 1975 1984 NobelPrize Screeningofhybridomacell Hybridomacell S S M M Myelomacell splenocyte HATselectivemedium 次黄嘌呤 hypoxanthine H 氨甲喋呤 aminopterin A 叶酸拮抗剂胸腺嘧啶核苷 thymidine T ScreeningwithHATselectivemedium H 次黄嘌呤 A 氨基喋呤 T 胸腺嘧啶 A Hypoxanthineguzninephosphoribosyltransferase 次嘌呤鸟嘌呤磷酸核糖转移酶 HGPRT 胸腺嘧啶激酶 TK Thymidinekinase Bcell HGPRT TK Myelomacell HGPRT TK live die Extrinsicpathway minor PRODUCTIONOFMONOCLONALANTIBODY HYBRIDOMATECHNOLOGY Applicat